Scatter-gather approach for parallel data transfer in a mass storage system

ABSTRACT

In an embodiment of the invention, an apparatus comprises: a first flash module comprising a first flash device; and a second flash module comprising a second flash device; wherein the first flash module and second flash module are coupled by a flash interconnect; wherein the first flash device is configured to store a first data stripe of a data and wherein the second flash device is configured to store a second data stripe of the data. In another embodiment of the invention, a method comprises: storing, in a first flash device in a first flash module, a first data stripe of a data; and storing, in a second flash device in a second flash module, a second data stripe of the data; wherein the first flash module and second flash module are coupled by a flash interconnect. In yet another embodiment of the invention, an article of manufacture comprises a non-transient computer-readable medium having stored thereon instructions that permit a method comprising: storing, in a first flash device in a first flash module, a first data stripe of a data; and storing, in a second flash device in a second flash module, a second data stripe of the data; wherein the first flash module and second flash module are coupled by a flash interconnect.

CROSS-REFERENCE(S) TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. Provisional Application 61/980,628, filed 17 Apr. 2014. This U.S. Provisional Application 61/980,628 is hereby fully incorporated herein by reference.

This application is a continuation in part of U.S. application Ser. No. 14/217,249 which claims the benefit of and priority to U.S. Provisional Application 61/799,949, filed 15 Mar. 2013. This U.S. Provisional Application 61/799,949 and U.S. application Ser. No. 14/217,249 are hereby fully incorporated herein by reference.

FIELD

Embodiments of the invention relate to storage systems. More particularly, embodiments of the invention relate to a method of implementing a faster data transfer in a mass storage system.

DESCRIPTION OF RELATED ART

The background description provided herein is for the purpose of generally presenting the context of the disclosure of the invention. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against this present disclosure of the invention.

Write data transfers in a conventional storage system are realized by two main operations, i.e. a data transfer from the host device to the system cache followed by the data transfer from the cache to a specific storage device. Similarly, a read transfer would entail that data retrieved from the storage device is primarily transferred to the system cache, after which data is forwarded to the host device. A common problem with this approach arises when large amount of data needs to be transferred by the system to non-volatile storage devices. Limitations on current technology allow programming or reading of data to/from storage devices to be only so fast. System performance, consequently, is tied to the slow mechanical storage devices. Subsequent requests from the host cannot be serviced by the system until the data transfer currently in service is completed. Thus, a primary concern for storage systems is to design certain methodologies that would allow the system to transfer subject data with minimal latency in spite of limitations on storage mediums.

A link between a computer system and other devices, such as flash devices, is generally called a channel. A channel is an independent unit and can function separately from the other channels coupled to the computer system and is capable of controlling data transfers on its assigned memory address space.

Consequently, the computer system can initiate concurrent data transfers across different memory address spaces through the different channels coupled to the computer system. Interleaving pertains to the method of accessing data in a parallel fashion by means of multiple channels. Striping means that data is divided into chunks of a certain size to be distributed to the devices across the storage array. The first stripe of data is sent to the first device, then the second stripe to the second device, and so on. The storage array has two critical parameters that have an important impact on the performance of the striped data in the storage array. The first key parameter is the stripe width of the storage array. Stripe width refers to the number of parallel stripes that can be written to or read from the storage array simultaneously. The second important parameter is the stripe size of the storage array, sometimes also referred to by the terms such as block size, chunk size, stripe length, or granularity. This term refers to the size of the stripes written to each device.

SUMMARY

Embodiments of the invention relate to storage systems. More particularly, embodiments of the invention relate to a method of implementing a faster data transfer in a mass storage system.

An embodiment of the invention is directed to the system performance limitation brought about by the slow storage devices. There is a need to make use of the benefits of striping and memory interleaving in improving the architecture of existing mass-storage systems in order to improve system performance.

An embodiment of the invention provides a method that allows faster data transfer to and from an array of storage devices. Employing the concepts of data striping and interleaving to achieve parallel data transfer significantly reduces memory latency. The entire storage array appears to the host device as a single storage device. Thus transfers employing the methods presented by embodiments of the invention appear to the host as the same as a conventional data transfer that was executed in significantly less time.

The architecture of a scalable mass storage system comprises an I/O (input/output) interface, a system bus, a local processor, a system cache, a plurality of DMA (Direct Memory Access) controllers coupled to a plurality of solid-state non-volatile memory devices. This achieves the concurrent data transfer across the storage array further reducing memory latency.

For Write to flash operations, data is divided into several portions called stripes. The local processor assigns a flash device address for each data stripe. A plurality of DMA engines are provided in each DMA controller. One or more engines across the system are issued with an instruction to control the transfer of a specific data stripe from the cache to the corresponding flash device. DMA engines work independently and the transfer of each corresponding data stripe is executed concurrently. A DMA engine is not tied to any specific memory address, and thus can be initiated to access any memory location in the cache. A data stripe is initially set aside in the DMA controller's data buffer. A write to flash operation is initiated by the DMA engine through the flash buffer chip. A high speed bus is provided to couple the flash buffer chip to the DMA engines. The flash buffer chip is used to forward flash specific command, address and raw data bytes from the DMA controller to the corresponding flash device. Data stripe in the DMA controller's data buffer is forwarded to the flash buffer chip via the high speed bus. The high speed bus supports burst transfers. A flash memory bus is provided to permit linking of multiple flash devices to the flash buffer chip. The flash buffer chip transmits data bytes over the flash memory bus. An internal buffer is provided in the flash buffer chip to facilitate the transmission of data bytes over the flash memory bus.

Alternatively, a Read from Flash command issued by the system host will result in the DMA engines receiving an instruction to retrieve a specific data stripe from the storage array. A DMA engine will initiate a read operation from the corresponding flash device through a flash buffer chip. Data stripe retrieved from the flash devices are transmitted over the flash memory bus and buffered by the flash buffer chip. The flash buffer chip forwards the data in its buffer to the DMA controller via a high speed bus. Lastly, the DMA engine forwards data stripe in the DMA controller's data buffer to the cache. With each DMA engine performing its corresponding data transfer for assigned data stripes, original data is reconstructed in the cache. The I/O interface, in turn, is in charge of the transfer of the reconstructed data in the cache to the requesting system host.

Several methods are provided to achieve concurrent data transfers:

(1) Scatter-Gather Approach through Device Striping: Interleaving is accomplished with the use of one or more engines in a single DMA controller. Striping of data is executed across several flash devices belonging to a single flash module and accessed through a single high speed bus.

(2) Scatter-Gather Approach through Group Striping: Interleaving is accomplished with the use of one or more engines in a single DMA controller. Striping of data is executed across several flash devices belonging to different flash modules and accessed through a single high speed bus.

(3) Scatter-Gather Approach through Bus Striping: Interleaving is accomplished with the use of several engines which may belong to one or more DMA controllers. Striping of data is executed across several flash devices belonging to different flash modules and accessed through several high speed busses.

Execution of one or a combination of the above mentioned approaches lends versatility and improved performance to the system.

In an embodiment of the invention, an apparatus comprises: a first flash module comprising a first flash device; and a second flash module comprising a second flash device; wherein the first flash module and second flash module are coupled by a flash interconnect; wherein the first flash device is configured to store a first data stripe of a data and wherein the second flash device is configured to store a second data stripe of the data.

In another embodiment of the invention, a method comprises: storing, in a first flash device in a first flash module, a first data stripe of a data; and storing, in a second flash device in a second flash module, a second data stripe of the data; wherein the first flash module and second flash module are coupled by a flash interconnect.

In yet another embodiment of the invention, an article of manufacture comprises a non-transient computer-readable medium having stored thereon instructions that permit a method comprising: storing, in a first flash device in a first flash module, a first data stripe of a data; and storing, in a second flash device in a second flash module, a second data stripe of the data; wherein the first flash module and second flash module are coupled by a flash interconnect.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one (several) embodiment(s) of the invention and together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the present invention may admit to other equally effective embodiments.

FIG. 1 is a block diagram illustrating an embodiment of a scalable mass storage system in accordance with the invention.

FIG. 2 is a block diagram illustrating a parallel data transfer across a plurality of flash devices in a flash bank, in accordance with an embodiment of the invention.

FIG. 3 is a block diagram illustrating a parallel data transfer across a plurality of flash devices belonging to different flash modules coupled through a single high speed bus, in accordance with an embodiment of the invention.

FIG. 4 is a block diagram illustrating a parallel data transfer across a storage array made up of a plurality of flash devices belonging to different flash modules coupled through a plurality of high speed busses, in accordance with an embodiment of the invention.

FIG. 5 is a block diagram illustrating a scalable mass storage system, in accordance with another embodiment of the present invention.

FIG. 6 is a block diagram illustrating a parallel data transfer across a plurality of flash devices in a data storage system, in accordance with another embodiment of the invention.

FIG. 7 is a block diagram illustrating a parallel data transfer across a plurality of flash devices in a data storage system, in accordance with yet another embodiment of the invention.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the various embodiments of the present invention. Those of ordinary skill in the art will realize that these various embodiments of the present invention are illustrative only and are not intended to be limiting in any way. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure.

In addition, for clarity purposes, not all of the routine features of the embodiments described herein are shown or described. One of ordinary skill in the art would readily appreciate that in the development of any such actual implementation, numerous implementation-specific decisions may be required to achieve specific design objectives. These design objectives will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine engineering undertaking for those of ordinary skill in the art having the benefit of this disclosure. The various embodiments disclosed herein are not intended to limit the scope and spirit of the herein disclosure.

Exemplary embodiments for carrying out the principles of the present invention are described herein with reference to the drawings. However, the present invention is not limited to the specifically described and illustrated embodiments. A person skilled in the art will appreciate that many other embodiments are possible without deviating from the basic concept of the invention. Therefore, the principles of the present invention extend to any work that falls within the scope of the appended claims.

As used herein, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items.

In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” (or “coupled”) is intended to mean either an indirect or direct electrical connection (or an indirect or direct optical connection). Accordingly, if one device is coupled to another device, then that connection may be through a direct electrical (or optical) connection, or through an indirect electrical (or optical) connection via other devices and/or other connections.

An embodiment of the invention relates to a method of transferring large blocks of data through a scatter-gather approach. The term “scatter” pertains to the distribution of the whole data to the entire mass storage system to virtually any flash device in the storage system. Likewise, the term “gather” relate to the fact that each small piece of data scattered throughout the storage system is retrieved to reconstruct the original data in the cache. The concepts of striping and interleaving are utilized to achieve the scatter-gather approach for the data transfer. An embodiment of the current invention achieves a parallel transfer of data by optimizing the architecture of the non-volatile storage system.

In an embodiment of the invention, in order to optimize flash device accesses, interleaving and striping methods are used in tandem. This method is implemented with the usage of multiple DMA engines. Each DMA engine works independently from other DMA engines performing the transfer of the other portions of the data. The amount of time to transfer data is minimized by as much as the number of DMA engines used. Additional features include flexibility in reconfiguring the stripe size and the number of interleaves depending on the user's application. An embodiment of the invention also provides a method for optimizing flash device accesses, comprising: interleaving and striping, in tandem, for a transfer of data the other portions of the data.

The figures and discussions provided in this document are meant to illustrate the invention being presented. It should not be construed as the only architecture to which the present invention can be utilized. The concepts and methods presented in this invention can be employed to other architectures in order to achieve a parallel data transfer that would enhance system performance.

A mass storage system of solid state non-volatile devices is illustrated in FIG. 1, in accordance with an embodiment of the invention. Request for a data transfer is issued by an external host 100, received by an internal host interface 101 and forwarded to the local processor 102 through a local bus 104. High-level requests are generated by the local processor 102 and issued to a DMA (Direct Memory Access) controller 105. The DMA controller 105 handles the data transfer without any further intervention from the local processor 102.

In the case of write data transfers, the DMA controller 105 fetches data from the volatile memory device (cache) 103 and transfer the data to one of the solid state non-volatile memory device (flash device) 113. A flash bank 112A comprises a plurality of flash devices connected to a flash buffer chip 110 through a single flash memory bus 111. A flash module 109A comprises a flash buffer chip 110 and a plurality of flash banks 112A-112C. Data is forwarded by the flash buffer chip 110 to a flash device 113 through the flash memory bus 111. Each flash module 109A-109C can be implemented in a single die/package. A plurality of flash modules 109A-109C is coupled to the DMA controller 105. The flash buffer chip of each flash module 109A-109C is coupled to the DMA controller 105 through the high speed busses 108A-108C. Each high speed bus coupled to the DMA controller 105 corresponds to one of the flash banks 112A-112C which are all coupled to the flash buffer chip 110. An internal buffer (not shown) is provided in the flash buffer chip 110 as a temporary holding area for data transmitted over the high speed busses 108A-108C. Additional details on an exemplary implementation of the high speed busses 108A-108C and the internal buffers provided in each flash buffer chip can be found in commonly-owned and commonly-assigned U.S. Pat. No. 8,447,908, issued on 21 May 2013, entitled MULTILEVEL MEMORY BUS SYSTEM FOR SOLID-STATE MASS STORAGE, which lists inventors Ricardo H. Bruce, Elsbeth Lauren T. Villapana, and Joel A. Baylon. U.S. Pat. No. 8,447,908 is hereby fully incorporated herein by reference.

An embodiment of the invention presents several options that could be implemented to enhance data transfer rates. Implementing one or a combination of presented options in a manner that suits the application will minimize required transfer time, allowing the system to overcome limiting factors brought about by the slow flash devices.

In one exemplary embodiment of the invention, data from the system host 100 that has been temporarily stored in the system cache 103 is divided into several portions and is transferred to the storage array 114 concurrently. The granularity of data portion could be any stripe size from 1 byte, 2 bytes to n-bytes. The transfer of each portion or stripe of data can be initiated by a command issued by the local processor 102 to the assigned DMA controller. The command received by the DMA controller 105 indicates the type of the operation and the addresses for the operation to occur. The operation may be a read or a write transfer while the address indicates the source and destination addresses of data to be transferred. The source address for write operations corresponds to the address in the cache 103 where the data stripe will be fetched by the DMA controller 105. The destination address, on the other hand, corresponds to the page address of a certain flash device 113 where the data will be written to. Similarly, the source address for read operations pertain to the page address in the flash device 113 where the data will be retrieved, and the destination address points to the cache 103 address where data will be transferred to. Taking into account the command overhead involved for each data transfer, the granularity of data should be chosen appropriately to provide an optimum system performance.

A DMA controller 105 comprises a plurality of DMA engines 106. Each DMA engine in the DMA controller 105 works independently. The DMA engines 106 facilitate the concurrent operations across the flash banks 112A-112C of each flash module 109A-109C coupled to the DMA controller 105 over the high speed busses 108A-108C. Since each DMA engine works independently, execution of the instructions issued by the local processor 102 for each DMA engine does not follow an exact sequence. That is, any DMA engine could initiate the first transfer of data from the cache 103 to the corresponding flash device in the storage array 114. A data buffer 107 is provided for each DMA controller 105. The data buffer 107 is shared by all DMA engines 106 in the DMA controller 105. The data buffer 107 is utilized by the DMA engines 106 for the data transfers between the non-volatile memory device 113 and volatile memory device 103. As soon as an engine receives a Write to Flash command from the local processor 102, the DMA controller 105 transfers the data from the volatile memory device 103 to the DMA controller's data buffer 107. This way, when the corresponding data transfer to the non-volatile memory device 113 is initiated by the DMA controller 105, data can be readily transferred over the high speed bus 108A or 108B or 108C. Likewise, upon receiving a Read from Flash command from the local processor 102, data retrieved from the addressed flash device 113 is buffered in the DMA controller's data buffer 107 from where data will be forwarded to the system cache 103.

A Discussion of data mapping over the storage array and the corresponding request generation is presented in greater detail in in commonly-owned and commonly-assigned U.S. Pat. No. 7,506,098, entitled OPTIMIZED PLACEMENT POLICY FOR SOLID STATE STORAGE DEVICES, issued on 17 Mar. 2009, which is hereby fully incorporated herein by reference.

A discussion of the command queueing for the DMA engines is presented in greater detail in commonly-owned and commonly-assigned U.S. patent application Ser. No. 14/690,339, entitled A SYSTEMATIC METHOD ON QUEUING OF DESCRIPTORS FOR MULTIPLE FLASH INTELLIGENT DMA ENGINE OPERATION, which lists inventors Marlon Basa Verdan and Rowenah Michelle Dy Jago-on, and this U.S. patent application Ser. No. 14/690,339 claims the benefit of and priority to U.S. Provisional Application 61/980,640, filed 17 Apr. 2014. U.S. Provisional Application 61/980,640 is hereby fully incorporated herein by reference. U.S. patent application Ser. No. 14/690,339, filed on 17 Apr. 2015, entitled A SYSTEMATIC METHOD ON QUEUING OF DESCRIPTORS FOR MULTIPLE FLASH INTELLIGENT DMA ENGINE OPERATION, which lists inventors Marlon Basa Verdan and Rowenah Michelle Dy Jago-on, is hereby fully incorporated herein by reference.

A discussion of the handshaking between the DMA controller and flash buffer chips over the Flashbus™ is presented in greater detail in the above-cited commonly-owned and commonly-assigned U.S. Pat. No. 8,447,908, issued on 21 May 2013, entitled MULTILEVEL MEMORY BUS SYSTEM FOR SOLID-STATE MASS STORAGE.

Scatter-Gather Approach Through Device Striping

A device striping approach for a write data transfer is illustrated in FIG. 2, in accordance with an embodiment of the invention, wherein the data transfer involves a single DMA controller 202 and a single flash bank 209A.

For a Write to Flash transfer, data 201 in the cache 200 is broken into m portions. Each data portion or stripe 201A-201C will be transferred across the flash devices 210A-210C of flash bank 209A in flash module 206. The local processor will issue an instruction to each of the n DMA engines 203A-203C in the DMA controller 202 to control the transfer of each portion of data 201A-201C from the cache 200. DMA Engine 203A will get an instruction from the local processor to transfer data stripe 201A to flash device 210A; DMA engine 203B will receive an instruction to transfer data stripe 201B to flash device 210B, and so on. If the data 201 is divided into portions which exactly match the number of DMA engines in the DMA controller 202, that is m=n, then each DMA engine 203A-203C will have exactly one data stripe to transfer. Otherwise, if the data 201 is split into several portions wherein the number of data stripes is greater than the number of engines, that is m>n, the local processor will assign the first n stripes to DMA engines 203A-203C. The assignment for the remaining stripes will again start from DMA engine 203A and so on until transfer for all stripes are delegated to a specific DMA engine. That is to say, transfer of data stripe n+1 will be assigned to engine 203A, data stripe n+2 to engine 203B and so on until data stripe m is assigned to a specific DMA engine. Furthermore, it is also possible that the number of flash devices in the flash bank 209A is not enough to accommodate all the m data. In which case, the local processor will assign the first x data stripes, wherein x is the number of flash devices in a flash bank, across all flash devices 210A-210C in the flash bank 209A, and then re-assign the succeeding data stripes x+1 to a different page across all flash devices 210A-210C of the same flash bank 209A, and so on until all m data stripes have been assigned to a specific flash device.

Upon receiving the Write to Flash request from the local processor, DMA engine 203A will fetch data stripe 201A from the cache 200 and transfer the data stripe 201A to buffer location 204A of the DMA controller 202. As soon as data stripe 201A is in buffer location 204A, DMA engine 203B in turn, initiates the transfer of data stripe 201B from the cache 200 to buffer location 204B. Each DMA engine 203A-203C alternately transfers assigned data stripe from the cache 200 to the data buffer of the DMA controller 202 until all data stripes have been fetched from the cache 200.

During the course of the transfer of the data stripes from the cache 200 to the DMA controller data buffer 204, another set of data transfer is taking place in the high speed bus 205A. Once data stripe 201A is in buffer location 204A, engine 203A will instruct the flash buffer chip 207 to initiate the write operation for flash device 210A. In this phase, DMA engine 203A likewise forwards data stripe 201A, from buffer location 204A to the flash buffer chip 207 internal buffer (not shown) through the high speed bus 205A in preparation for the pending write operation to flash device 210A. Once the flash buffer chip 207 has sent to the flash device 210A the appropriate flash command and the corresponding flash address, the flash buffer chip 207 will start the transmission of data stripe 201A, which is currently residing in the internal buffer, to flash device 210A over the flash memory bus 208.

Likewise, DMA engine 203B will initiate the transfer of data stripe 201B over to flash device 210B. The transfer of data stripe 201B from buffer location 204B in the DMA controller 202 to the flash buffer chip 207 occurs in parallel to the programming of data stripe 201A to flash device 210A. The process above repeats until all data stripes that comprise the entire data 201 has been distributed over the flash devices 210A-210C of flash module 206 as designated by the local processor.

In a similar fashion, a Read from Flash request from the external host device for the data 201 will result to the local processor generating instructions for each DMA engine 203A-203C in the DMA controller 202 to retrieve each corresponding data stripe 201A-201C from flash devices 210A-210C. To illustrate, engine 203A will trigger flash buffer chip 207 to initiate a read operation for flash device 210A to retrieve data stripe 201A. While flash device 210A is busy acquiring and relocating data stripe 201A from its storage array to the device's data register, engine 203B triggers flash buffer chip 207 to initiate the read operation for flash device 210B to retrieve data stripe 201B. All other engines, will likewise initiate the read operation for each corresponding flash device to retrieve all data stripes. Once requested data is already residing in the internal buffer of the flash buffer chip 207, the corresponding DMA engine will initiate the transfer of the data from the flash buffer chip 207 to a free buffer location in the data buffer 204. That is to say, engine 203A will request flash buffer chip 207 to forward data in its internal buffer that corresponds to data stripe 201A over the high speed bus 205A. Data stripe 201A transmitted over the high speed bus 205A will be kept in the data buffer location 204A. DMA Engine 203A will then forward acquired data stripe 201A from buffer location 204A to the cache 200. Correspondingly, each DMA engine 203B-203C will forward subsequent data stripes 201B-201C from flash devices 210B-210C to the cache 200. This results to the reconstruction of the original data 201 in the cache 200.

As mentioned before, the execution of the instructions issued by the local processor for each DMA engine does not follow an exact order, thus the sequence of data transfer is not restricted to the discussion provided above. DMA Engine 203C could initiate the transfer for data stripe 201C from the cache 200 to the DMA controller data buffer 204 before DMA engine 203A sets off the transfer of data stripe 201A. Data transfer for any data stripe 201A-201C from the cache 200, for that matter, could be executed first by the corresponding DMA engine 203A-203C. Furthermore, as implied by the term “scatter”, the data stripe assignment of each DMA controller, and consequently of each flash device, does not necessarily have to be sequential as illustrated in the discussion. Data stripe 201A could be programmed to flash device 210C instead, while data stripe 201B is programmed to flash device 210A, whereas data stripe 201C is programmed into flash device 210B.

Moreover, the device striping mechanism can be executed to other flash banks 209B-209C, and is not limited to the first flash bank 209A of flash module 206. If the local processor opts to distribute the data 201 over flash bank 209B, high speed bus 205B will be used for the transfer between the DMA controller 202 and the flash buffer chip 207. Likewise, device striping with flash bank 209C will entail the use of the high speed bus 205C.

Scatter-Gather Approach Through Group Striping

The parallel data transfer offered by the device striping transfer is further enhanced by the group striping method. The group striping approach involves data transfer across flash banks 308A-308C, each flash bank belonging to flash module 306A-306C respectively and connected through a single high speed bus 305A, as shown in FIG. 3, in accordance with an embodiment of the invention.

For a Write to Flash data transfer, data 301 in the cache 300 is broken into m portions. Each data stripe 301A-301C will be transferred across the flash banks 308A-308C coupled to the DMA controller 302 through the high speed bus 305A. The local processor will issue an instruction for each DMA engine 303A-303C in the DMA controller 302 to transfer one portion of the data 301 from the cache 300. DMA Engine 303A will receive an instruction from the local processor to transfer data stripe 301A to flash device 311A of flash bank 308A, DMA engine 303B will be designated to transfer data stripe 301B to flash device 311B of flash bank 308B, DMA engine 303C will be designated to transfer data stripe 301C to flash device 311C of flash bank 308C, and so on.

Upon receiving the Write to Flash request from the local processor, engine 303A will fetch data stripe 301A from the cache 300 and transfer the data stripe 301A to buffer location 304A. As soon as data stripe 301A is in buffer location 304A, engine 303B in turn initiates the transfer of data stripe 301B from cache 300 to buffer location 304B. Each engine 303A-303C alternately transfer assigned data stripe from the cache 300 to the data buffer of the DMA controller 302 until all data stripes have been fetched from the cache 300.

While each data stripe from the cache 300 is being transferred to the DMA controller data buffer, another set of data transfer is taking place over the high speed bus 305A. In the instance that data stripe 301A is in buffer location 304A, DMA engine 303A will instruct flash buffer chip 307A to initiate the write operation for flash device 311A. In this phase, engine 303A likewise forwards data stripe 301A, from buffer location 304A to the internal buffer (not shown) of flash buffer chip 307A, through the high speed bus 305A, in preparation for the pending write operation to flash device 311A. As soon as data stripe 301A is transferred to flash buffer chip 307A, DMA engine 303A releases ownership of the high speed bus 305A as DMA engine 303B takes over the high speed bus 305A. In the same way, DMA engine 303B will initiate the write operation for flash device 311B through flash buffer chip 307B. Data stripe 301B will be forwarded from buffer location 304B to the internal buffer of flash buffer chip 307B. Similarly, DMA engine 303C transfers data stripe 301C to the internal buffer of flash buffer chip 307C once the DMA engine 303C gains control of the high speed bus 305A. Each DMA engine replicates the process discussed in order to transfer each DMA engine's corresponding data stripe to the designated flash device.

Flash buffer chip 307A, having initiated the write operation for flash device 311A, will transmit data stripe 301A from its internal data buffer over the flash memory bus 314A. Flash buffer chip 307B, as well, will transmit data stripe 301B to flash device 311B over the flash memory bus 314B once data stripe 301B is transferred to its internal buffer. All flash buffer chips involved in the data transfer will go through the same process. Thus, flash buffer chip 307C will likewise transfer data stripe 301C to flash device 311C through flash memory bus 314C.

Data transfer from the flash buffer chips 307A-307C to the corresponding flash devices 311A-311C is executed in parallel since different flash buffer chips and consequently different flash memory busses are utilized.

In a similar fashion, a Read from Flash request for the data 301 will result to the local processor generating instructions for each DMA engine 303A-303C in the DMA controller 302 to retrieve each corresponding data stripe 301A-301C from flash devices 311A-311C. DMA Engine 303A will initiate a read operation for flash device 311A to retrieve data stripe 301A, through flash buffer chip 307A. At the same time, DMA engine 303B instructs flash buffer chip 307B to initiate the read operation for flash device 311B to retrieve data stripe 301B. At the same time, DMA engine 303C instructs flash buffer chip 307C to initiate the read operation for flash device 311C to retrieve data stripe 301C. All other DMA engines will likewise initiate the read operation for each corresponding flash device to retrieve all related data stripes. Once requested data is already residing in the internal buffer of the flash buffer chip, the corresponding DMA engine will initiate the transfer of the data from the flash buffer chip to a free buffer location in the DMA controller's 302 data buffer. Specifically, engine 303A will request flash buffer chip 307A to forward the data in its internal buffer which corresponds to data stripe 301A. Data stripe 301A transmitted over high speed bus 305A will be kept in buffer location 304A, from which location DMA engine 303A will forward acquired data stripe 301A to the cache 300. Similarly, each DMA engine 303B-303C will forward subsequent data stripes from flash buffer chips 307B-307C to the cache 300. This results to the reconstruction of the original data 301 in the cache 300. It is important to note, however, that the cache address where the data 301 will be reconstructed does not necessarily have to be the same cache address used during the write operation.

It should also be noted that the group striping approach is not limited to the use of the first flash device 311A-311C of each flash bank 308A-308C as what is presented in the discussion above. The local processor can choose any flash device from 311A-311C, 312A-312C to 313A-313C from each flash bank 308A-308C as the end destination for the data stripes. Correspondingly, the DMA engines, acting based on the instructions from the local processor, will transfer their designated data stripe from the cache to the assigned flash device. That is to say that the Write to Flash or Read from Flash data transfers discussed above could have involved flash devices 312A-312C or even flash devices 313A-313C. Moreover, the group striping approach, as discussed above could be executed utilizing other flash banks of flash modules 306A-306C, such as flash banks 309A-309C or flash banks 310A-310C. Group striping method involving flash banks 309A-309C would entail the use of the high speed bus 305C, as this high speed flash bus 305C is coupled with flash banks 310A-310C utilizing high speed bus 305C. Furthermore, the local processor can incorporate the device striping concept with the group striping approach as described in the succeeding discussions.

For Write to Flash data transfers, data 301 in the cache 300 is broken into m portions. Each data stripe 301A-301C will be transferred across the flash banks 308A-308C coupled to the DMA controller 302 through the high speed bus 305A. The local processor will issue an instruction for each engine 303A-303C in the DMA controller 302 to transfer one portion of data 301 from the cache 300. Engine 303A will receive an instruction from the local processor to transfer data stripe 301A to flash device 311A of flash bank 308A, engine 303B will be designated to transfer data stripe 301B to flash device 312B of flash bank 308B, and so on; engine 303C will transfer data stripe 301C to flash device 313C of flash bank 308C.

Upon receiving the Write to Flash request from the local processor, engine 303A will fetch data stripe 301A from the cache 300 and transfer it to buffer location 304A of the DMA controller data buffer. As soon as data stripe 301A is in buffer location 304A, engine 303B in turn initiates the transfer of data stripe 301B from cache 300 to buffer location 304B. Each engine 303A-303C alternately transfer assigned data stripe from the cache 300 to the data buffer of the DMA controller 302 until all data stripes have been fetched from the cache 300.

While each data stripe from the cache 300 is being transferred to the DMA controller data buffer, another set of data transfer is taking place in the high speed bus 305A. In the instance that data stripe 301A is in buffer location 304A, engine 303A will instruct flash buffer chip 307A to initiate the write operation for flash device 311A. In this phase, engine 303A likewise forwards data stripe 301A, from buffer location 304A to the internal buffer of flash buffer chip 307A, through the high speed bus 305A, in preparation for the pending write operation to flash device 311A. As soon as data stripe 301A is transferred to flash buffer chip 307A, engine 303A releases ownership of the high speed bus 305A as engine 303B takes over the high speed bus 305A. In the same way, engine 303B will initiate the write operation for flash device 312B through flash buffer chip 307B. Data stripe 301B will be forwarded from buffer location 304B to the internal buffer of flash buffer chip 307B. Similarly, engine 303C transfers data stripe 301C to the internal buffer of flash buffer chip 307C once engine 303C gains control of the high speed bus 305A. Each DMA engine will replicate the process discussed above to transfer each DMA engine's corresponding data stripe to the designated flash device.

Flash buffer chip 307A, having initiated the write operation for flash device 311A, will transmit data stripe 301A over the flash memory bus 314A. Flash buffer chip 307B, on the other hand, will transmit data stripe 301B to flash device 312B over the flash memory bus 314B once data stripe 301B is transferred to its internal buffer. All flash buffer chips involved in the data transfer will go through the same process discussed. Thus, flash buffer chip 307C will likewise transfer data stripe 301C to flash device 313C through flash memory bus 314C.

Data transfer from the flash buffer chips 307A-307C to the corresponding flash devices 311A, 312B to 313C is likewise executed in parallel. The latter discussion illustrates that the chosen end destination for each data stripe need not be the same flash device of each flash module. That is, in flash module 306A the first flash device 311A in the flash bank is chosen as the end destination for a particular data stripe, while in flash module 306B flash device 312B, which is the second flash device in the flash bank, is selected as the end destination for the corresponding data stripe and so on.

In a similar fashion, a Read from Flash request for the data 301 will result to the local processor generating instructions for each engine 303A-303C in the DMA controller 302 to retrieve each corresponding data stripe 301A-301C from flash devices 311A, 312B to 313C. Engine 303A will initiate a read operation for flash device 311A to retrieve data stripe 301A. At the same time, engine 303B initiates the read operation for flash device 312B to retrieve data stripe 301B. All other engines, will likewise initiate the read operation for each corresponding flash device to retrieve all related data stripes. Once requested data is already residing in the internal buffer of the flash buffer chip, the corresponding engine will initiate the transfer of the data from the flash buffer chip to a free buffer location in the DMA controller's data buffer. Specifically, engine 303A will request flash buffer chip 307A to forward over the high speed bus 305A the data in its internal buffer which corresponds to data stripe 301A. Engine 303A will then forward acquired data stripe 301A from buffer location 304A to the cache 300. Correspondingly, each engine 303B-303C will forward subsequent data stripes from flash buffer chips 307B-307C to the cache 300. This results to the reconstruction of the original data 301 in the cache 300.

Scatter-Gather Approach Through Bus Striping

Bus striping, as illustrated in FIG. 4, is another method used to achieve faster data transfer, in accordance with an embodiment of the invention. This method is faster than the group striping approach because this method utilizes the flash buffer chips simultaneously across all busses.

For Write to Flash data transfers, data 401 in the cache 400 is broken into m stripes. Each data stripe 402A-402C will be distributed to the flash devices 411A-411C within each flash module 408A-408C across the storage array 407 coupled to the DMA controllers 403A-403C through high speed busses 406A-406C. The local processor will issue an instruction for each DMA engine 404A-404C in the DMA controller 403A-403C to transfer a stripe of the data 401 in the cache 400. DMA Engine 404A (in DMA controller 403A) will transfer data stripe 402A to flash device 411A, DMA engine 404B (in DMA controller 403B) will transfer data stripe 402B to flash device 411B, DMA engine 404C (in DMA controller 403C) will transfer data stripe 402C to flash device 411C, and so on.

Upon receiving the Write to Flash request from the local processor, engine 404A will fetch data stripe 402A from the cache 400 and transfer the data stripe 402A to the data buffer 405A within the DMA controller 403A. As soon as data stripe 402A is transferred, engine 404B in turn initiates the transfer of data stripe 402B from the cache 400 to the data buffer 405B within the DMA controller 403B. Each time that a transfer of a data stripe from the cache to the data buffer is completed, another engine will initiate the transfer for the next data stripe.

Immediately after a certain defined portion of each data stripe from the cache 400 is transferred to the data buffer 405A-405C within the DMA controller 403A-403C, another set of data transfer is to take place in the high speed bus 406A-406C. In the instance that a certain defined portion of the data stripe 402A is in the data buffer 405A within the DMA controller 403A, engine 404A will instruct flash buffer chip 409A to initiate the write operation for flash device 411A. In this phase, engine 404A likewise forwards data stripe 402A from the data buffer 405A within the DMA controller 403A to the data buffer within the flash buffer chip 409A through high speed bus 406A. This transfer between two data buffers is in preparation for the pending write operation to flash device 411A. While this operation is taking place in high speed bus 406A, a similar operation is taking place in high speed bus 406B and high speed bus 406C. These operations occur simultaneously because each DMA controller 403A-403C with its corresponding high speed bus 406A-406C is running independently from each other.

Flash buffer chips 409A, having initiated the write operation for flash device 411A, will transmit data stripe 402A over the flash memory bus 410A. Flash buffer chip 409B, as well, will transmit data stripe 402B to flash device 411B over the flash memory bus 410B. All flash buffer chips involved in the data transfer will go through the same process.

Data transfer from the flash buffer chips 409A-409C to the corresponding flash devices 411A-411C are executed in parallel since different flash buffer chips 409A-409C and consequently different flash memory busses 410A-410C are utilized. That is to say, transfer of data stripes 402B-402C can commence once any of these data stripes 402B-402C gets transferred to flash buffer chips 409B-409C.

In a similar process, a Read from Flash request for the data 401 will result to the local processor generating instructions for each DMA engine 404A-404C in the DMA controller 403A-403C to retrieve simultaneously each corresponding data stripe 402A-402C from the flash devices 411A-411C. After a certain defined portion of the requested data stripes 402A-402C are transferred to the internal buffers of the flash buffer chips 409A-409C, the corresponding DMA engines 404A-404C will initiate the transfer of the data from the flash buffer chips 409A-409C to the data buffer 405A-405C within the DMA controller 403A-403C. DMA Engine 404A (in DMA controller 403A) will request flash buffer chip 409A to forward over the high speed bus 406A the data in its internal buffer which corresponds to data stripe 402A. DMA Engine 404A will then forward the acquired data stripe 402A from the data buffer 405A within the DMA controller 403A to the cache 400. Each DMA engine 404B-404C will forward the subsequent data stripes from flash buffer chips 409B-409C to the cache 400. This results to the reconstruction of the original data 401 in the cache 400. It is important to note, however, that the cache address where the data 401 will be reconstructed does not necessarily have to be the same cache address used during the write operation.

It should also be noted that the bus striping approach could use any flash device other than flash devices 411A-411C of flash modules 408A-408C as the end destination for any of the data stripes 402A-402C. Furthermore, the bus striping approach is not limited to the use of the first flash modules 408A-408C from each high speed bus 406A-406C. The local processor can choose any flash modules, and consequently any flash device integrated on said flash modules coupled through the high speed busses for the data transfer at hand. In further aspect of the invention, a bus striping approach can be executed with a single DMA controller, in which case the data transfer could involve a single flash module or several flash modules utilizing several high speed busses.

Simply put, data stripes 402A-402C in the cache 400 can be transferred to any flash device in the storage array 407 by using one or any combination of the different methods as discussed above. This gives the local processor maximum control on how the data will be transferred and retrieved.

A mass storage system 550 of solid state non-volatile devices is illustrated in FIG. 5, in accordance with another embodiment of the invention. Request for a data transfer is issued by an external host 500, received by an internal host interface 501 and forwarded to the local processor 502 through a local bus 504. High-level requests are generated by the local processor 502 and issued to a DMA (Direct Memory Access) controller 505. The DMA controller 505 handles the data transfer without any further intervention from the local processor 502. DMA controller 505 performs data transfers to and from a storage array 514 in the storage system 550 (storage apparatus 550).

In the case of write data transfers, the DMA controller 505 fetches data from the volatile memory device (cache) 503 and transfer the data to one of the solid state non-volatile memory device (flash device) 513. A flash bank 512A comprises a plurality of flash devices connected to a flash buffer chip 510 through a single flash memory bus 511. The storage array 514 comprises a plurality of flash modules such as, for example, flash modules 509A and 509B. The flash module 509A comprises a flash buffer chip 510 and a plurality of flash banks 512A-512C. Data is forwarded by the flash buffer chip 510 to a flash device 513 through the flash memory bus 511. Each flash module 509A-509B (and/or other flash modules, such as flash modules 509C and 509D) can be implemented in a single die/package. A plurality of flash modules 509A-509B is coupled to the DMA controller 505, while the as flash modules 509C and 509D which are coupled to the DMA controller 555 in storage system 550.

Similarly, the flash module 509B comprises a flash buffer chip 560 and a plurality of flash banks 565A-565C. Data is forwarded by the flash buffer chip 560 to a flash device 570 through the flash memory bus 572.

In an embodiment of the invention, the storage array 514 of storage system 550 includes a flash interconnect 580 which can be a network-like fabric similar to the flash interconnect disclosed in commonly-owned and commonly-assigned U.S. application Ser. No. 14/217,161, which is entitled MULTI-CHIP MEMORY CONTROLLER CONNECTED TO A PLURALITY OF MEMORY ARRAY VIA COMMUNICATION BUS, with named inventors Ricardo H. Bruce, Jarmie De La Cruz Espuerta, and Marlon Basa Verdan. U.S. application Ser. No. 14/217,161 is hereby fully incorporated herein by reference. For example, the flash interconnect 580 disclosed herein can be embodied as a network of flashbus and flashbus controllers (and/or as a point-to-point serial bus topology and/or network-like fabric), similar to the flash interconnect disclosed in commonly-owned and commonly-assigned. U.S. patent application Ser. No. 14/217,161.

The flash modules 509A and 509B are coupled by the flash interconnect 580. The DMA controller 505 is coupled via flash interconnect 580 to the flash modules 509A and 509B. The flash modules that are coupled by the flash interconnect 580 may vary in number as noted by, for example, the dot symbols 652. Similarly, the DMA controllers that are coupled to the local bus 504 and to respective flash modules may also vary in number as noted by, for example, the dot symbols 553.

The flash interconnect 580 comprises a channel 582. The flash buffer chips 510 and 560 are coupled by the channel 582 to the DMA controller 505. The channel 582 comprises one or more point-to-point lines which can be, for example, one flashbus or a plurality of flashbuses for transmitting signals such as command, status, response, address, and data bytes. In an embodiment of the invention, the channel 582 comprises a plurality of high speed buses 508A-508C. The high speed buses in the channel 582 may vary in number as noted by, for example, the dot symbols 554.

In an embodiment of the invention, the flash interconnect 580 comprises a network-like fabric interconnect or a point-to-point serial bus topology, or a network comprising a plurality of flashbus controllers and at least one flashbus that connects at least two of the plurality of flashbus controllers. A flash interconnect 580 can also include a plurality of flashbus controllers, with one of the flashbus controllers coupled via channel 582 to the flash buffer chip 510 and another one of the flashbus controllers coupled via channel 582 to flash buffer chip 560. An example of a flashbus controller is disclosed in U.S. patent application Ser. No. 14/217,161. Flashbus controllers can receive and transmit command, status, response, address, and data bytes. Therefore, the channel 582 also receives and transmits command, status, response, address, and data bytes to and from the flash modules 509A and 509B.

Similarly, a flash interconnect 585 (similar in features to the flash interconnect 580) is coupled to and between the flash modules 509C and 509D.

The flash buffer chip 510 of the flash module 509A is coupled to the DMA controller 505 through the high speed busses 508A-508C of channel 582 of flash interconnect 580. Each high speed bus coupled to the DMA controller 505 corresponds to one of the flash banks 512A-512C which are all coupled to the flash buffer chip 510. An internal buffer (not shown) is provided in the flash buffer chip 510 as a temporary holding area for data transmitted over the high speed busses 508A-508C. Additional details on an exemplary implementation of the high speed busses 508A-508C and the internal buffers provided in each flash buffer chip can be found in commonly-owned and commonly-assigned U.S. Pat. No. 8,447,908, issued on 21 May 2013, entitled MULTILEVEL MEMORY BUS SYSTEM FOR SOLID-STATE MASS STORAGE, which lists inventors Ricardo H. Bruce, Elsbeth Lauren T. Villapana, and Joel A. Baylon. U.S. Pat. No. 8,447,908 is hereby fully incorporated herein by reference.

The flash buffer chip 560 of the flash module 509B is also coupled to the DMA controller 505 through the high speed busses 508A-508C of channel 582 of flash interconnect 580. Each high speed bus coupled to the DMA controller 505 corresponds to one of the flash banks 565A-565C which are all coupled to the flash buffer chip 560. An internal buffer (not shown) is provided in the flash buffer chip 560 as a temporary holding area for data transmitted over the high speed busses 508A-508C.

An embodiment of the invention presents several options that could be implemented to enhance data transfer rates. Implementing one or a combination of presented options in a manner that suits the application will minimize required transfer time, allowing the system to overcome limiting factors brought about by the slow flash devices.

In one exemplary embodiment of the invention, data from the system host 500 that has been temporarily stored in the system cache 503 is divided into several portions and is transferred to the storage array 514 concurrently. The granularity of data portion could be any stripe size from 1 byte, 2 bytes to n-bytes. The transfer of each portion or stripe of data can be initiated by a command issued by the local processor 502 to the assigned DMA controller. The command received by the DMA controller 505 indicates the type of the operation and the addresses for the operation to occur. The operation may be a read or a write transfer while the address indicates the source and destination addresses of data to be transferred. The source address for write operations corresponds to the address in the cache 503 where the data stripe will be fetched by the DMA controller 505. The destination address, on the other hand, corresponds to the page address of a certain flash device 513 in flash module 509A where the data will be written to (or to the page address of another certain flash device 570 in flash module 509B where the data will instead be written to). Similarly, the source address for read operations pertain to the page address in the flash device 513 (or the source address for read operations pertain to the page address in the flash device 570) where the data will be retrieved, and the destination address points to the cache 503 address where data will be transferred to. Taking into account the command overhead involved for each data transfer, the granularity of data should be chosen appropriately to provide an optimum system performance.

A DMA controller 505 comprises a plurality of DMA engines 506. Each DMA engine in the DMA controller 505 works independently. The DMA engines 506 facilitate the concurrent operations across the flash banks 512A-512C of flash module 509A (and/or across the flash banks 565A-565C of flash module 509B) coupled to the DMA controller 505 over the high speed busses 508A-508C. Since each DMA engine works independently, execution of the instructions issued by the local processor 502 for each DMA engine does not follow an exact sequence, as similarly described above in other embodiments of a storage system. That is, any DMA engine could initiate the first transfer of data from the cache 503 to the corresponding flash device in the storage array 514, as similarly described above in other embodiments of a storage system. A data buffer 507 is provided for each DMA controller 505. The data buffer 507 is shared by all DMA engines 506 in the DMA controller 505. The data buffer 507 is utilized by the DMA engines 506 for the data transfers between the non-volatile memory devices 513 (in flash module 509A) and non-volatile memory devices 570 (in flash module 509B) and volatile memory device 503. As soon as a DMA engine (e.g., any of DMA engine 0 through DMA engine n−1 in DMA controller 505) receives a Write to Flash command from the local processor 502, the DMA controller 505 transfers the data from the volatile memory device 503 to the DMA controller's data buffer 507. This way, when the corresponding data transfer to the non-volatile memory device 513 (or/and non-volatile memory device 570) is initiated by the DMA controller 505, data can be readily transferred over the high speed bus 508A or 508B or 508C. Likewise, upon receiving a Read from Flash command from the local processor 502, data retrieved from the addressed flash device 513 (and/or from the addresses flash device 570) is buffered in the DMA controller's data buffer 507 from where data will be forwarded to the system cache 503.

A Discussion of data mapping over the storage array 514 and the corresponding request generation is presented in greater detail in commonly-owned and commonly-assigned U.S. Pat. No. 7,506,098, entitled OPTIMIZED PLACEMENT POLICY FOR SOLID STATE STORAGE DEVICES, issued on 17 Mar. 2009, which is hereby fully incorporated herein by reference.

A discussion of the command queueing for the DMA engines 506 is presented in greater detail in commonly-owned and commonly-assigned U.S. patent application Ser. No. 14/690,339, filed on 17 Apr. 2015, entitled A SYSTEMATIC METHOD ON QUEUING OF DESCRIPTORS FOR MULTIPLE FLASH INTELLIGENT DMA ENGINE OPERATION, which lists inventors Marlon Basa Verdan and Rowenah Michelle Dy Jago-on, and this U.S. patent application Ser. No. 14/690,339 claims the benefit of and priority to U.S. Provisional Application 61/980,640, filed 17 Apr. 2014. U.S. Provisional Application 61/980,640 is hereby fully incorporated herein by reference. U.S. patent application Ser. No. 14/690,339, filed on 17 Apr. 2015, entitled A SYSTEMATIC METHOD ON QUEUING OF DESCRIPTORS FOR MULTIPLE FLASH INTELLIGENT DMA ENGINE OPERATION, which lists inventors Marlon Basa Verdan and Rowenah Michelle Dy Jago-on, is hereby fully incorporated herein by reference.

A discussion of the handshaking between a DMA controller (e.g., DMA controller 505) and flash buffer chips (e.g., flash buffer chips 510 and 560) over the Flashbus™ is presented in greater detail in the above-cited commonly-owned and commonly-assigned U.S. Pat. No. 8,447,908, issued on 21 May 2013, entitled MULTILEVEL MEMORY BUS SYSTEM FOR SOLID-STATE MASS STORAGE.

A device striping approach for a write data transfer is illustrated in FIG. 6, in accordance with another embodiment of the invention. In an embodiment of the invention, the storage system 650 comprises a storage array with a plurality of flash modules 606A, 606B, and 606C. The write data transfer in the storage system 650 involves using a volatile memory device 600, a single DMA controller 602, and at least one or more of the plurality of flash modules 606A, 606B, and 606C. In the storage system 650, the number of flash modules may vary as noted by, for example, the dot symbols 652.

In an embodiment of the invention, the DMA controller 602 is coupled via a flash interconnect 680 to the plurality of flash modules 606A, 606B, and 606C. The flash interconnect 680 is similar in features as the flash interconnect 580 in FIG. 5 and can be a network-like fabric similar to the flash interconnect disclosed in above-mentioned commonly-owned and commonly-assigned U.S. application Ser. No. 14/217,161. The flash interconnect 680 disclosed herein can be embodied as a network of flashbus and flashbus controllers (and/or as a point-to-point serial bus topology and/or network-like fabric), similar to the flash interconnect disclosed in U.S. patent application Ser. No. 14/217,161.

The flash interconnect 680 comprises a channel 682 and is coupled to the buffer chip 607A (in flash module 606A), flash buffer chip 607B (in flash module 606B), and flash buffer 607C (in flash module 606C). The DMA controller 602 is coupled via channel 682 to the flash modules 606A-606C. In particular, the DMA controller 602 is coupled via channel 682 to the flash buffer chips 607A-607C in flash modules 606A-606C, respectively. The channel 682 comprises one or more point-to-point lines which can be, for example, one flashbus or a plurality of flashbuses for transmitting signals such as command, status, response, address, and data bytes. As an example, the channel 682 is formed by a plurality of high speed buses 605A-605C between DMA controller 602 and flash module 606A, a plurality of high speed buses 605D-605F between flash module 606A and flash module 606B, and a plurality of high speed buses 605G-605I between flash module 606B and flash module 606C. The high speed buses in the channel 682 may vary in number as noted by, for example, dot symbols 685.

For a Write to Flash transfer, data 601 in the cache 600 is broken into m portions. Each data portion or stripe 601A-601C will be transferred across the flash devices in the storage system 650 in various ways of striping. The local processor will issue an instruction to each of the n DMA engines 603A-603C in the DMA controller 602 to control the transfer of each portion of data 601A-601C from the cache 600. DMA Engine 603A will get an instruction from the local processor to transfer data stripe 601A to flash device 611A; DMA engine 603B will receive an instruction to transfer data stripe 601B to flash device 612A; DMA engine 603C will receive an instruction to transfer data stripe 601C to flash device 613A, and so on. If the data 601 is divided into portions which exactly match the number of DMA engines in the DMA controller 602, that is m=n, then each DMA engine 603A-603C will have exactly one data stripe to transfer. Otherwise, if the data 601 is split into several portions wherein the number of data stripes is greater than the number of engines, that is m>n, the local processor will assign the first n stripes to DMA engines 603A-603C. The assignment for the remaining stripes will again start from DMA engine 603A and so on until transfer for all stripes are delegated to a specific DMA engine. That is to say, transfer of data stripe n+1 will be assigned to engine 603A, data stripe n+2 to engine 603B and so on until data stripe m is assigned to a specific DMA engine. Furthermore, it is also possible that the number of flash devices in the flash bank 608A is not enough to accommodate all the m data. In which case, the local processor will assign the first x data stripes, wherein x is the number of flash devices in a flash bank, across all flash devices 611A, 612A, and 613A in the flash bank 608A, and then re-assign the succeeding data stripes x+1 to a different page across all flash devices 611A, 612A, 613A of the same flash bank 608A, and so on until all m data stripes have been assigned to a specific flash device.

Upon receiving the Write to Flash request from the local processor, DMA engine 603A will fetch data stripe 601A from the cache 600 and transfer the data stripe 601A to buffer location 604A of the DMA controller 602. As soon as data stripe 601A is in buffer location 604A, DMA engine 603B in turn, initiates the transfer of data stripe 601B from the cache 600 to buffer location 604B. Each DMA engine 603A-603C alternately transfers assigned data stripe from the cache 600 to the data buffer of the DMA controller 602 until all data stripes have been fetched from the cache 600.

During the course of the transfer of the data stripes from the cache 600 to the DMA controller data buffer 604, another set of data transfer is taking place in the high speed bus 605A. Once data stripe 601A is in buffer location 604A, engine 603A will instruct the flash buffer chip 607A to initiate the write operation for flash device 611A. In this phase, DMA engine 603A likewise forwards data stripe 601A, from buffer location 604A to the flash buffer chip 607A internal buffer (not shown) through the high speed bus 605A in preparation for the pending write operation to flash device 611A. Once the flash buffer chip 607A has sent to the flash device 611A the appropriate flash command and the corresponding flash address, the flash buffer chip 607A will start the transmission of data stripe 601A, which is currently residing in the internal buffer, to flash device 611A over the flash memory bus 614A.

Likewise, DMA engine 603B will initiate the transfer of data stripe 601B over to flash device 612A. The transfer of data stripe 601B from buffer location 604B in the DMA controller 602 to the flash buffer chip 607A occurs in parallel to the programming of data stripe 601A to flash device 611A. The process above repeats until all data stripes that comprise the entire data 601 has been distributed over the flash devices 611A, 612A, and 613A of flash module 606A as designated by the local processor.

In a similar fashion, a Read from Flash request from the external host device for the data 601 will result to the local processor generating instructions for each DMA engine 603A-603C in the DMA controller 602 to retrieve each corresponding data stripe 601A-601C from flash devices 611A, 612A, and 613A. To illustrate, engine 603A will trigger flash buffer chip 607A to initiate a read operation for flash device 611A to retrieve data stripe 601A. While flash device 611A is busy acquiring and relocating data stripe 601A from its storage array to the device's data register, engine 603B triggers flash buffer chip 607A to initiate the read operation for flash device 612A to retrieve data stripe 601B. All other engines, will likewise initiate the read operation for each corresponding flash device to retrieve all data stripes. Once requested data is already residing in the internal buffer of the flash buffer chip 607A, the corresponding DMA engine will initiate the transfer of the data from the flash buffer chip 607A to a free buffer location in the data buffer 604. That is to say, engine 603A will request flash buffer chip 607A to forward data in its internal buffer that corresponds to data stripe 601A over the high speed bus 605A. Data stripe 601A transmitted over the high speed bus 605A will be kept in the data buffer location 604A. DMA Engine 603A will then forward acquired data stripe 601A from buffer location 604A to the cache 600. Correspondingly, each DMA engine 603B-603C will forward subsequent data stripes 601B-601C from flash devices 612A and 613A to the cache 600. This results to the reconstruction of the original data 601 in the cache 600.

As mentioned before, the execution of the instructions issued by the local processor for each DMA engine does not follow an exact order, thus the sequence of data transfer is not restricted to the discussion provided above. DMA Engine 603C could initiate the transfer for data stripe 601C from the cache 600 to the DMA controller data buffer 604 before DMA engine 603A sets off the transfer of data stripe 601A. Data transfer for any data stripe 601A-601C from the cache 600, for that matter, could be executed first by the corresponding DMA engine 603A-603C. Furthermore, as implied by the term “scatter”, the data stripe assignment of each DMA controller, and consequently of each flash device, does not necessarily have to be sequential as illustrated in the discussion. Data stripe 601A could be programmed to flash device 613A instead, while data stripe 601B is programmed to flash device 611A, whereas data stripe 601C is programmed into flash device 612A.

Moreover, the device striping mechanism can be executed to other flash banks 609A and 610A, and is not limited to the first flash bank 608A of flash module 606A. If the local processor opts to distribute the data 601 over flash bank 609A, high speed bus 605B (and flash memory bus 690) will be used for the transfer between the DMA controller 602 and the flash buffer chip 607A. Likewise, device striping with flash bank 610A will entail the use of the high speed bus 605C (and flash memory bus 691).

Moreover, the device striping mechanism can be executed to flash devices in flash banks in other flash memory modules 606B or 606C, and is not limited to the first flash module 606A. If the local processor opts to distribute the data 601 over flash devices 611B, 612B, and 613B in flash bank 608B of flash module 606B, high speed bus 605D (and flash memory bus 614B) will be used for the transfer between the DMA controller 602 and the flash buffer chip 607B. Likewise, device striping with flash bank 609B will entail the use of the high speed bus 605E (and flash memory bus 692). Likewise, device striping with flash bank 610B will entail the use of the high speed bus 605F (and flash memory bus 693).

Likewise, device striping with flash bank 608C in flash module 606C will entail the use of the high speed bus 605G (and flash memory bus 614C). Likewise, device striping with flash bank 609C will entail the use of the high speed bus 605H (and flash memory bus 694). Likewise, device striping with flash bank 610C will entail the use of the high speed bus 605I (and flash memory bus 695).

In another embodiment of the invention, the data 601 can be striped across flash devices that are in different flash modules. For example, the data 601 can be striped across devices in flash modules 606A-606C. Data stripe 601A can be programmed in a flash device (e.g., flash device 611A in flash bank 608A) in flash module 606A. Data stripe 601B can be programmed in a flash device (e.g., flash device 611B in flash bank 608B) in flash module 606B. Data stripe 601C can be programmed in a flash device (e.g., flash device 611C in flash bank 608C) in flash module 606C. The data stripes 601A-601 c can be programmed in other flash devices in any of the flash banks in flash modules 606A-606B.

Bus striping, as illustrated in FIG. 7, is another method used to achieve faster data transfer, in accordance with an embodiment of the invention. This method in the system 750 is faster than the group striping approach because this method utilizes the flash buffer chips simultaneously across all busses.

For Write to Flash data transfers, data 701 in the cache 700 is broken into m stripes. Each data stripe 702A-702C will be distributed to the flash devices 711A-711C within each flash module 708A-708C across the storage array 707 coupled to the DMA controllers 703A-703C through high speed busses 706A-706C, respectively. The local processor will issue an instruction for each DMA engine 704A-704C in the DMA controller 703A-703C to transfer a stripe of the data 701 in the cache 700 via bus 750. DMA Engine 704A (in DMA controller 703A) will transfer data stripe 702A to flash device 711A, DMA engine 704B (in DMA controller 703B) will transfer data stripe 702B to flash device 711B, DMA engine 704C (in DMA controller 703C) will transfer data stripe 702C to flash device 711C, and so on. As will be discussed below, system 750 includes flash interconnects that permit the data 701 to be striped in other distributed flash modules.

Upon receiving the Write to Flash request from the local processor, engine 704A will fetch data stripe 702A from the cache 700 and transfer the data stripe 702A to the data buffer 705A within the DMA controller 703A. As soon as data stripe 702A is transferred, engine 704B in turn initiates the transfer of data stripe 702B from the cache 700 to the data buffer 705B within the DMA controller 703B. Each time that a transfer of a data stripe from the cache to the data buffer is completed, another engine will initiate the transfer for the next data stripe.

Immediately after a certain defined portion of each data stripe from the cache 700 is transferred to the data buffer 705A-705C within the DMA controller 703A-703C, respectively, another set of data transfer is to take place in the high speed bus 706A-706C. In the instance that a certain defined portion of the data stripe 702A is in the data buffer 705A within the DMA controller 703A, engine 704A will instruct flash buffer chip 709A to initiate the write operation for flash device 711A. In this phase, engine 704A likewise forwards data stripe 702A from the data buffer 705A within the DMA controller 703A to the data buffer within the flash buffer chip 709A through high speed bus 706A. This transfer between two data buffers is in preparation for the pending write operation to flash device 711A. While this operation is taking place in high speed bus 706A, a similar operation is taking place in high speed bus 706B and high speed bus 706C. These operations occur simultaneously because each DMA controller 703A-703C with its corresponding high speed bus 706A-706C is running independently from each other.

Flash buffer chip 709A, having initiated the write operation for flash device 711A, will transmit data stripe 702A over the flash memory bus 752A. Flash buffer chip 709B, as well, will transmit data stripe 702B to flash device 711B over the flash memory bus 752B. All flash buffer chips involved in the data transfer will go through the same process.

Data transfer from the flash buffer chips 709A-709C to the corresponding flash devices 710A-710C are executed in parallel since different flash buffer chips 709A-709C and consequently different flash memory busses 752A-752C are utilized. That is to say, transfer of data stripes 702B-702C can commence once any of these data stripes 702B-702C gets transferred to flash buffer chips 709B-709C.

In a similar process, a Read from Flash request for the data 701 will result to the local processor generating instructions for each DMA engine 704A-704C in the corresponding DMA controller 703A-703C to retrieve simultaneously each corresponding data stripe 702A-702C from the flash devices 711A-711C. After a certain defined portion of the requested data stripes 702A-702C are transferred to the internal buffers of the flash buffer chips 709A-709C, the corresponding DMA engines 704A-704C will initiate the transfer of the data from the flash buffer chips 709A-709C to the data buffer 705A-705C within the DMA controller 703A-703C, respectively. DMA Engine 704A (in DMA controller 703A) will request flash buffer chip 709A to forward over the high speed bus 706A the data in its internal buffer which corresponds to data stripe 702A. DMA Engine 704A will then forward the acquired data stripe 702A from the data buffer 705A within the DMA controller 703A to the cache 700. Each DMA engine 704B-704C will forward the subsequent data stripes from flash buffer chips 709B-709C to the cache 700. This results to the reconstruction of the original data 701 in the cache 700. It is important to note, however, that the cache address where the data 701 will be reconstructed does not necessarily have to be the same cache address used during the write operation.

It should also be noted that the bus striping approach could use any flash device other than flash devices 711A-711C of flash modules 708A-708C, respectively, as the end destination for any of the data stripes 702A-702C. Furthermore, the bus striping approach is not limited to the use of the first flash modules 708A-708C from each high speed bus 706A-706C. The local processor can choose any flash modules, and consequently any flash device integrated on said flash modules coupled through the high speed busses for the data transfer at hand. In further aspect of the invention, a bus striping approach can be executed with a single DMA controller, in which case the data transfer could involve a single flash module or several flash modules utilizing several high speed busses.

Simply put, data stripes 702A-702C in the cache 700 can be transferred to any flash device in the storage array 707 by using one or any combination of the different methods as discussed above. This gives the local processor maximum control on how the data will be transferred and retrieved.

In an embodiment of the invention, the system 750 comprises the DMA controller 703A coupled via flash interconnect 760A to the flash modules 708A and 762A, the DMA controller 703B coupled via flash interconnect 760B to the flash modules 708B and 762B, and the DMA controller 703C coupled via flash interconnect 760C to the flash modules 708C and 762C. The flash interconnects 760A-760C include the same features as the flash interconnects that are disclosed in FIG. 5 or 6. The flashbus modules coupled via a flash interconnect to a DMA controller can vary in number as noted by, for example, dot symbols 756. The DMA controllers in the system 750 can also vary in number as noted by, for example, dot symbols 757.

The device striping mechanism can be executed to flash devices in flash banks in other flash memory modules 762A-762C, and is not limited to the flash modules 708A-708C. If the local processor opts to distribute the data 701 over flash devices 770A-770C of flash modules 762A-762C, respectively, respective high speed bus 772A (of flash interconnect 760A) and flash memory bus 774A will be used for the transfer between the DMA controller 703A and the flash buffer chip 775A (of flash module 762A). Likewise, device striping with flash module 762B will entail the use of the high speed bus 772B (of flash interconnect 760B) and flash memory bus 774B. Likewise, device striping with flash module 762C will entail the use of the high speed bus 772C (of flash interconnect 760C) and flash memory bus 774C.

Foregoing described embodiments of the invention are provided as illustrations and descriptions. They are not intended to limit the invention to precise form described. In particular, it is contemplated that functional implementation of invention described herein may be implemented equivalently in hardware, software, firmware, and/or other available functional components or building blocks, and that networks may be wired, wireless, or a combination of wired and wireless.

It is also within the scope of the present invention to implement a program or code that can be stored in a non-transient machine-readable (or non-transient computer-readable medium) having stored thereon instructions that permit a method (or that permit a computer) to perform any of the inventive techniques described above, or a program or code that can be stored in an article of manufacture that includes a non-transient computer readable medium on which computer-readable instructions for carrying out embodiments of the inventive techniques are stored. Other variations and modifications of the above-described embodiments and methods are possible in light of the teaching discussed herein.

The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.

These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation. 

What is claimed is:
 1. An apparatus, comprising: a volatile memory configured to store data; a Direct Memory Access (DMA) controller directly coupled by a local bus to the volatile memory; a first flash module comprising a first flash buffer chip, a first flash memory bus, and a first flash bank comprising a first plurality of flash devices including a first flash device, wherein the first plurality of flash devices are coupled by the first flash memory bus to the first flash buffer chip in the first flash module; and a second flash module comprising a second flash buffer chip, a second flash memory bus, and a second flash bank comprising a second plurality of flash devices including a second flash device, wherein the second plurality of flash devices are coupled by the second flash memory bus to the second flash buffer chip in the second flash module; wherein the first flash buffer chip in the first flash module and the second flash buffer chip in the second flash module are directly coupled by a flash interconnect to the DMA controller; wherein the flash interconnect comprises a first plurality of high speed buses that is directly coupled to the first flash buffer chip in the first flash module and to the DMA controller; wherein the flash interconnect comprises a second plurality of high speed buses that is directly coupled to the second flash buffer chip in the second flash module and to the first flash buffer chip in the first flash module; wherein the first flash device is configured to store a first data stripe of the data and wherein the second flash device is configured to store a second data stripe of the data; wherein the DMA controller comprises a DMA controller data buffer, a first DMA engine, and a second DMA engine; wherein the DMA controller data buffer comprises a first buffer location and a second buffer location; wherein the first DMA engine transfers the first data stripe between the first flash device and the first buffer location when a predetermined portion of data stripes is stored in the first flash buffer chip; and wherein the second DMA engine transfers the second data stripe between the second flash device and the second buffer location when a predetermined portion of data stripes is stored in the second flash buffer chip.
 2. The apparatus of claim 1, wherein the flash interconnect comprises a fabric interconnect.
 3. The apparatus of claim 1, wherein the flash interconnect comprises a point-to-point serial bus topology.
 4. The apparatus of claim 1, wherein the flash interconnect comprises a plurality of flash memory bus controllers and at least one flash memory bus that connects at least two of the plurality of flash memory bus controllers.
 5. The apparatus of claim 1, further comprising: a second DMA controller coupled by a second flash interconnect to a third flash module.
 6. The apparatus of claim 1, further comprising a plurality of independent DMA controllers.
 7. The apparatus of claim 1 wherein each of the plurality of independent DMA controllers includes a plurality of DMA engines and a data buffer.
 8. The apparatus of claim 1, wherein each of the plurality of DMA controllers is coupled with a shared data cache.
 9. A method, comprising: storing data in a volatile memory; wherein the volatile memory is directly coupled by a local bus to a Direct Memory Access (DMA) controller; wherein the DMA controller is directly coupled by a flash interconnect to a first flash module and to a second flash module; wherein the first flash module comprises a first flash buffer chip, a first flash memory bus, and a first flash bank comprising a first plurality of flash devices including a first flash device, wherein the first plurality of flash devices are coupled by the first flash memory bus to the first flash buffer chip in the first flash module; wherein the second flash module comprises a second flash buffer chip, a second flash memory bus, and a second flash bank comprising a second plurality of flash devices including a second flash device, wherein the second plurality of flash devices are coupled by the second flash memory bus to the second flash buffer chip in the second flash module; wherein the first flash buffer chip in the first flash module and the second flash buffer chip in the second flash module are directly coupled by the flash interconnect to the DMA controller; wherein the flash interconnect comprises a first plurality of high speed buses that is directly coupled to the first flash buffer chip in the first flash module and to the DMA controller; wherein the flash interconnect comprises a second plurality of high speed buses that is directly coupled to the second flash buffer chip in the second flash module and to the first flash buffer chip in the first flash module; storing, in the first flash device in the first flash module, a first data stripe of the data; and storing, in the second flash device in the second flash module, a second data stripe of the data; wherein the DMA controller comprises a DMA controller data buffer, a first DMA engine, and a second DMA engine; wherein the DMA controller data buffer comprises a first buffer location and a second buffer location; wherein the first DMA engine transfers the first data stripe between the first flash device and the first buffer location when a predetermined portion of data stripes is stored in the first flash buffer chip; and wherein the second DMA engine transfers the second data stripe between the second flash device and the second buffer location when a predetermined portion of data stripes is stored in the second flash buffer chip.
 10. The method of claim 9, wherein the flash interconnect comprises a fabric interconnect.
 11. The method of claim 9, wherein the flash interconnect comprises a point-to-point serial bus topology.
 12. The method of claim 9, wherein the flash interconnect comprises a plurality of flash memory bus controllers and at least one flash memory bus that connects at least two of the plurality of flash memory bus controllers.
 13. The method of claim 9, wherein a second DMA controller is coupled by a second flash interconnect to a third flash module.
 14. The method of claim 9 wherein the first DMA engine transfers the first data stripe between the first flash device and the first buffer location when a single data stripe is stored in the first flash buffer chip.
 15. An article of manufacture, comprising: a non-transitory computer-readable medium having stored thereon instructions to permit an apparatus to perform a method comprising: storing data in a volatile memory; wherein the volatile memory is directly coupled by a local bus to a Direct Memory Access (DMA) controller; wherein the DMA controller is directly coupled by a flash interconnect to a first flash module and to a second flash module; wherein the first flash module comprises a first flash buffer chip, a first flash memory bus, and a first flash bank comprising a first plurality of flash devices including a first flash device, wherein the first plurality of flash devices are coupled by the first flash memory bus to the first flash buffer chip in the first flash module; wherein the second flash module comprises a second flash buffer chip, a second flash memory bus, and a second flash bank comprising a second plurality of flash devices including a second flash device, wherein the second plurality of flash devices are coupled by the second flash memory bus to the second flash buffer chip in the second flash module; wherein the first flash buffer chip in the first flash module and the second flash buffer chip in the second flash module are directly coupled by the flash interconnect to the DMA controller; wherein the flash interconnect comprises a first plurality of high speed buses that is directly coupled to the first flash buffer chip in the first flash module and to the DMA controller; wherein the flash interconnect comprises a second plurality of high speed buses that is directly coupled to the second flash buffer chip in the second flash module and to the first flash buffer chip in the first flash module; storing, in the first flash device in the first flash module, a first data stripe of the data; and storing, in the second flash device in the second flash module, a second data stripe of the data; wherein the DMA controller comprises a DMA controller data buffer, a first DMA engine, and a second DMA engine; wherein the DMA controller data buffer comprises a first buffer location and a second buffer location; wherein the first DMA engine transfers the first data stripe between the first flash device and the first buffer location when a predetermined portion of data stripes is stored in the first flash buffer chip; and wherein the second DMA engine transfers the second data stripe between the second flash device and the second buffer location when a predetermined portion of data stripes is stored in the second flash buffer chip.
 16. The article of manufacture of claim 15, wherein the flash interconnect comprises a fabric interconnect. 